Macrophage reprogramming by negatively-charged membrane phospholipids controls infection

Extracellular vesicles (ECV) are heterogeneous membrane-enclosed structures containing proteins, nucleic acids and lipids that participate in intercellular communication by transferring their content to recipient cells. Although most of the attention has been directed at the biological effect of proteins and microRNA, the contribution of phospholipids present in ECV on cellular activation has not been extensively addressed. Here we investigated the biological effect of phosphatidylserine (PS) and phosphatidylcholine (PC), two phospholipids highly abundant in ECV. A transcriptomic analysis revealed that about 4,700 genes were specifically modified by exposing peritoneal macrophages to PS or PC liposomes in vivo. Among them, the expression of several chemokines and cytokines was highly upregulated by PS liposome treatment, translating into a massive neutrophil infiltration into the peritoneum capable of neutralizing a septic polymicrobial insult. Both the L and D stereoisomers of PS induced the same response, suggesting that the effect was related to the negative charge of the phospholipid head. We concluded that an increase in the internal negative charge of the cell triggers a signaling cascade activating an innate immune response capable of controlling infection. Overall design: Total RNA isolated from peritoneal cells obtained by lavage from CD-1 mice intraperitoneally injected for 1 hour with POPC liposomes (400 µg at 1 mg/ml, n=3 mice), POPS liposomes (400 µg at 1 mg/ml, n=3 mice), or PBS (400 µl, controls n=3 mice)